1. Field of Industrial Applications
The present invention relates to a surge tank structure in an intake manifold.
2. Related Art
In general, an intake manifold for use in an automobile gasoline or diesel engine has such a structure as shown in FIG. 9, where a plurality of branch tubes 2 are joined at one end to a cylinder head mounting flange 4 provided for installation on a cylinder head and at the other end to a surge tank 3. FIG. 10 illustrates an enlarged cross sectional view of the joint between the branch tubes 2 and the surge tank 3. Each branch tube 2 is connected and inserted into the surge tank 3. The inner wall for accepting the leading end of the branch tube 2 has a horn-like region 51 formed by changing the diameter for the purpose of moderating a change of the cross section so that the load of a suction caused by abrupt change in the cross section can be reduced. The surge tank 3 is fabricated by casting using a core for shaping the horn-like regions 51, and the use of such a core increases production costs.
To reduce costs, a modification has been proposed, which is shown in FIG. 11 and FIG. 12, which is a cross sectional view taken along the line XII--XII of FIG. 11. Here, the leading end of each branch tube 2 is flared or enlarged in its diameter to produce a horn-like flared or enlarged region 2a and is then mounted to a surge tank 3. The surge tank 3 comprises two separable components, a lower member 52 and an upper member 53. More specifically, after the branch tubes 2 having the horn-like flared or enlarged regions 2a have been set in their position, the upper member 53 is joined to the lower member 52 to complete the surge tank 3. The joint between the branch tube 2 and the two tank members 52 and 53 includes semi-circular and straight regions, thus requiring higher degrees of the roundness of the overall dimensions of the branch tubes 2 and a more accurate machining of the joining portions of the lower member 52 and the upper member 53 to the branch tubes 2. In addition, a set of pins 54 is needed for positioning the lower member 52 and the upper member 53, thereby increasing the manufacturing cost. Moreover, any displacement between the branch tubes 2 and the two tank members 52 and 53, may disadvantageously cause the condensed liquid or blow-by oil 0 deposited on the bottom of the lower member 52 to remain there since the condensed liquid may not be sucked into the branch tubes 2.